Gas burners, in wide use for decades, are fueled by combustible gases with or without being mixed with air. Very commonly used combustible gases includes natural gas and liquefied propane (LP) gas. (Liquefied propane is stored under pressure in liquid form and becomes gaseous when fed to a gas burner at lower pressure.) Gas burners are useful to heat water, heat a room or a building, carry out industrial processes and for many other purposes.
Known gas burners include at least two broad configurations. In one, holes are formed in a sheet metal or cast body and define a straight line, a circle or some other shape. U.S. Pat. No. 5,406,703 (Haen et al.) discloses a burner of this type. In such configuration, holes constitute a relatively small percentage of the overall body area.
Another known configuration uses a porous flame handler. Burners of this type are disclosed in U.S. Pat. No. 4,657,506 (Ihlenfield et al.) and U.S. Pat. No. 5,165,887 (Ahmady). The burner disclosed in the Ihlenfield et al. patent has a rigid inner support member through which gas is fed. Such member has a multiplicity of small openings which cover the entire axial and circumferential extent of that portion of the member which forms the burner.
The rigid support member is surrounded by a cylinder-shaped woven metal fabric tube spaced radially outwardly from the support member. Gas fed into the support member exits the member openings and the openings in the metal fabric tube and combustion is supported on the exterior of such tube.
The burner disclosed in the Ahmady patent has an inner element comprised of woven ceramic cloth wrapped around a supporting wire mesh cylinder. Gaseous fuel having no air mixed with it is fed into such cylinder. (The patent describes that if the ceramic cloth is wrapped in several layers, no support is needed.)
This inner element is received in and surrounded by a metal tube spaced from the element to define a plenum between them. There are separate feed ports for gas and air. In one configuration, gas is fed into the inner element, air to the plenum and combustion occurs in the plenum, i.e., on the outer surface of the inner element and between such element and the surrounding metal tube. In another configuration, gas is fed to the plenum, air is fed into the inner element and combustion occurs on the inner surface of the inner element.
While the burners disclosed in the Ihlenfield et al. and Ahmady patents are presumed to be suitable for their intended purposes, they are not without disadvantages. A seeming disadvantage of the Ihlenfield et al. burner involves the fuel feed rate and the burnoff rate. If more gas is supplied in a effort to increase heat output, it would appear that at some gas feed rate, the flame "lifts away" from the mesh. It is understood that this may actually diminish heat output. And at some even-higher gas feed rate, the burner is likely to extinguish completely.
Another disadvantage of the Ihlenfield et al. burner and, apparently, of that version of the Ahmady burner in which combustion occurs in the plenum is that there is no provision for "afterburning" the products of combustion.
Still another disadvantage of the Ihlenfield et al. and Ahmady burners is that neither is well suited for use with a conventional cooking devices such as a stove top. This is not surprising in view of the fact that they are configured for specific applications.
A seeming disadvantage of the burner disclosed in the Ahmady patent is its nominal specified gas/air feed rate cannot be exceeded. Since combustion occurs within the surrounding closed metal tube, i.e., in an unvented space, gas and air should not be fed in at a rate which unduly pressurizes the tube. There is apparent risk of tube rupture. Exhaust gas emission may be unduly elevated, particularly with regard to the proportion of carbon monoxide contained in such emission.
An improved gas burner which addresses disadvantages of known porous burners would be an important advance in this field of technology.